Photoexcited CRY2 interacts with CIB1 to regulate transcription and floral initiation in Arabidopsis

Cryptochromes (CRY) are photolyase-like blue-light receptors that mediate light responses in plants and animals. How plant cryptochromes act in response to blue light is not well understood. We report here the identification and characterization of the Arabidopsis CIB1 (cryptochrome-interacting basic-helix-loop-helix) protein. CIB1 interacts with CRY2 (cryptochrome 2) in a blue light-specific manner in yeast and Arabidopsis cells, and it acts together with additional CIB1-related proteins to promote CRY2-dependent floral initiation. CIB1 binds to G box (CACGTG) in vitro with a higher affinity than its interaction with other E-box elements (CANNTG). However, CIB1 stimulates FT messenger RNA expression, and it interacts with chromatin DNA of the FT gene that possesses various E-box elements except G box. We propose that the blue light-dependent interaction of cryptochrome(s) with CIB1 and CIB1-related proteins represents an early photoreceptor signaling mechanism in plants.     

Roles of the two Drosophila CRYPTOCHROME structural domains in circadian photoreception

CRYPTOCHROME (CRY) is the primary circadian photoreceptor in Drosophila. We show that CRY binding to TIMELESS (TIM) is light-dependent in flies and irreversibly commits TIM to proteasomal degradation. In contrast, CRY degradation is dependent on continuous light exposure, indicating that the CRY-TIM interaction is transient. A novel cry mutation (cry(m)) reveals that CRY's photolyase homology domain is sufficient for light detection and phototransduction, whereas the carboxyl-terminal domain regulates CRY stability, CRY-TIM interaction, and circadian photosensitivity. This contrasts with the function of Arabidopsis CRY domains and demonstrates that insect and plant cryptochromes use different mechanisms.     

拟南芥隐花色素突变体抑制子的筛选及其表型分析

隐花色素（cryptochrome,简称CRY）是与DNA光解酶氨基酸序列高度同源的黄素蛋白,但不具有光解酶活性。拟南芥的隐花色素家族中隐花色素1（CRY1）主要抑制下胚轴伸长,隐花色素2（CRY2）主要调节光周期开花,并且这两个光受体具有部分重叠的功能。cry1cry2双突变体在长日条件下比野生型晚开花。采用激活标签的方法,在cry1cry2双突变体背景下筛选到一个早开花突变体scc17-D (suppressor of cry1cry2#17-Dominant)。TAIL-PCR结果表明,scc17-D突变体的T-DNA插入在第一条染色体上的At1g25440和At1g25450两个基因之间。scc17-D突变体表现出植株矮化、叶片变小、果荚变小和子叶表皮细胞形状发生改变等性状。     

Direct interaction of Arabidopsis cryptochromes with COP1 in light control development

Arabidopsis seedling photomorphogenesis involves two antagonistically acting components, COP1 and HY5. COP1 specifically targets HY5 for degradation via the 26S proteasome in the dark through their direct physical interaction. Little is known regarding how light signals perceived by photoreceptors are transduced to regulate COP1. Arabidopsis has two related cryptochromes (cry1 and cry2) mediating various blue/ultraviolet-A light responses. Here we show that both photoactivated cryptochromes repress COP1 activity through a direct protein-protein contact and that this direct regulation is primarily responsible for the cryptochrome-mediated blue light regulation of seedling photomorphogenic development and genome expression profile.     

Orchestrated transcription of key pathways in Arabidopsis by the circadian clock

Like most organisms, plants have endogenous biological clocks that coordinate internal events with the external environment. We used high-density oligonucleotide microarrays to examine gene expression in Arabidopsis and found that 6% of the more than 8000 genes on the array exhibited circadian changes in steady-state messenger RNA levels. Clusters of circadian-regulated genes were found in pathways involved in plant responses to light and other key metabolic pathways. Computational analysis of cycling genes allowed the identification of a highly conserved promoter motif that we found to be required for circadian control of gene expression. Our study presents a comprehensive view of the temporal compartmentalization of physiological pathways by the circadian clock in a eukaryote.     

Light-responsive cryptochromes from a simple multicellular animal, the coral Acropora millepora

Hundreds of species of reef-building corals spawn synchronously over a few nights each year, and moonlight regulates this spawning event. However, the molecular elements underpinning the detection of moonlight remain unknown. Here we report the presence of an ancient family of blue-light-sensing photoreceptors, cryptochromes, in the reef-building coral Acropora millepora. In addition to being cryptochrome genes from one of the earliest-diverging eumetazoan phyla, cry1 and cry2 were expressed preferentially in light. Consistent with potential roles in the synchronization of fundamentally important behaviors such as mass spawning, cry2 expression increased on full moon nights versus new moon nights. Our results demonstrate phylogenetically broad roles of these ancient circadian clock-related molecules in the animal kingdom.     

Enhanced fitness conferred by naturally occurring variation in the circadian clock

Natural variation in clock parameters is necessary for the circadian clock to contribute to organismal fitness over a broad geographic range. Considerable variation is evident in the period, phase, and amplitude of 150 Arabidopsis accessions, and the period length is correlated with the day length at the latitude of origin, implying the adaptive significance of correctly regulated circadian timing. Quantitative trait loci analysis of recombinant inbred lines indicates that multiple loci interact to determine period, phase, and amplitude. The loss-of-function analysis of each member of the ARABIDOPSIS PSEUDO-RESPONSE REGULATOR family suggests that they are candidates for clock quantitative trait loci.     

Darwinian selection on a selfing locus

The shift to self-pollination is one of the most prevalent evolutionary transitions in flowering plants. In the selfing plant Arabidopsis thaliana, pseudogenes at the SCR and SRK self-incompatibility loci are believed to underlie the evolution of self-fertilization. Positive directional selection has driven the evolutionary fixation of pseudogene alleles of SCR, leading to substantially reduced nucleotide variation. Coalescent simulations indicate that this adaptive event may have occurred very recently and is possibly associated with the post-Pleistocene expansion of A. thaliana from glacial refugia. This suggests that ancillary morphological innovations associated with self-pollination can evolve rapidly after the inactivation of the self-incompatibility response.     

烟属起源与分子系统进化的研究进展

烟草是重要的经济作物和植物研究中的模式植物,其起源、进化以及多倍体的演化一直受到研究者的重视.系统整理了烟属起源、进化关系、祖先种等最新研究成果,对比了这些新观点与Goodspeed经典烟属起源、进化理论的异同.     

Ecology. Stalking the wild mustard

Arabidopsis thaliana is not just for plant biologists anymore. A few intrepid ecologists and evolutionary biologists are now touting its merits as a system in which to study the genetic basis of the traits they study. The newly completed genome sequence is allowing researchers to connect the genotype--an organism's particular mix of genes--with its phenotype--how that organism develops and acts--in ways that have not been possible in other organisms whose genetics are not as well known.     

植物 Tetraspanins 蛋白的研究进展

Tetraspanins(TETs)是一大类进化性保守的、具有4次跨膜结构域的蛋白超家族,广泛分布于所有多细胞生物体中。对植物TETs蛋白的结构特征、系统进化,以及模式植物拟南芥的TETs蛋白超家族(At TET1~17)和番茄Tetraspanin3蛋白的生物功能进行综述,旨在为今后更好地研究植物TETs蛋白超家族提供参考。     

光敏色素互作因子(PIFs)对植物生长发育的调控

光敏色素相互作用因子(PIFs)属于拟南芥bHLH转录因子家族的第15亚族,是光信号响应过程中的关键负调控因子。光激活的光敏色素通过促进PIFs蛋白降解,直接或间接抑制它们与DNA的结合,从而实现光对植物生长发育的调控。研究发现PIFs在调控种子萌发、幼苗形态建成、避荫反应、昼夜节律以及各种植物激素响应过程中起着重要作用。此外,PIFs作为细胞信号传导的"枢纽"具有更为广泛的作用,能够整合不同信号,精细调控整个转录网络。     

Photic induction of mPer1 and mPer2 in cry-deficient mice lacking a biological clock

Mice lacking mCry1 and mCry2 are behaviorally arrhythmic. As shown here, cyclic expression of the clock genes mPer1 and mPer2 (mammalian Period genes 1 and 2) in the suprachiasmatic nucleus and peripheral tissues is abolished and mPer1 and mPer2 mRNA levels are constitutively high. These findings indicate that the biological clock is eliminated in the absence of both mCRY1 and mCRY2 (mammalian cryptochromes 1 and 2) and support the idea that mammalian CRY proteins act in the negative limb of the circadian feedback loop. The mCry double-mutant mice retain the ability to have mPer1 and mPer2 expression induced by a brief light stimulus known to phase-shift the biological clock in wild-type animals. Thus, mCRY1 and mCRY2 are dispensable for light-induced phase shifting of the biological clock.     

马铃薯StKN1基因的cDNA克隆与分析

植物同源异型枢基因(Homeobox gene,HBG)广泛存在,是一类重要的转录因子编码基因,在生物进化中具有很强的保守性。利用GenBank登录的拟南芥、苜蓿、豌豆、烟草、番茄等同源异型枢基因保守区序列设计简并引物,通过RT-PCR技术,从马铃薯萌动的幼芽中获得了一个homeobox的cDNA基因,命名为StKN1,GenBank登录号为DQ494855.1。该基因片段长971 bp,经序列分析比对,与其他植物的HBG具有很高的序列相似性。系统进化分析将StKN1基因归入homeobox KNOX基因家族。     

植物多倍体研究进展

多倍体是高等植物染色体进化的一个显著特征 ,约 70 %的被子植物在其进化过程中曾经历过一次或多次多倍化事件。多倍体在植物中广泛存在 ,由于其具有一些独特的性质 ,已逐渐成为广大育种学家研究的热点。文中介绍了植物多倍体起源、诱导方法、鉴定方法及多倍体应用等方面的研究进展 ,并对植物多倍体研究过程中所存在的几个问题进行了探讨。     

Arabidopsis kin help keep genetics studies all in the family

An unobtrusive weed often found at roadsides and other disturbed sites, Arabidopsis thaliana has risen from its humble roots to become the model organism, or "lab rat," for studying plant molecular biology. Now, by comparing the genetic makeup and characteristics of A. thaliana to its cousins, evolutionary biologists can discern how the plant has changed through time.     

单宁对反刍动物影响的研究进展

单宁又称植物多酚,是存在于植物体内的一类多元酚化合物,系植物进化过程中产生的一种自身保护性次生物质。在传统的动物营养学研究中,单宁一直被认为是一种抗营养因子,在生产实践中也采取许多消除其抗营养作用的方法。但对于反刍动物来说,单宁能降低瘤胃内蛋白质的降解率,进而提高反刍动物对优质蛋白质的利用率,此外单宁还是良好的抗氧化剂和天然驱虫剂,适当应用可以提高反刍动物的生产性能。不同的反刍动物对饲料中的单宁有不同的耐受性,应该深入研究家养条件下单宁对各种家养反刍动物的影响,以合理利用饲料资源,提高动物健康和生产能力。